sudo apt-get install redmine redmine-mysql
Then once that is installed add the following line to /etc/apache2/mods-available/passenger.conf
PassengerDefaultUser www-data
Then add the following lines in /etc/apache2/sites-available/default
<Directory /var/www/redmine>
RailsBaseURI /redmine
PassengerResolveSymlinksInDocumentRoot on
</Directory>
Then enable the passenger module for apache by running:
sudo a2enmod passenger
After that add the redmine softlink in the /var/www directory:
cd /var/www
sudo ln -s /usr/share/redmine/public redmine
Then you should be able to access it from http://localhost/redmine. Default username and password is admin:admin.